Question

为什么我的数组包含所有null？在这个代码区域

 while (st.hasMoreTokens()) {
            tokFix[i] = st.nextToken();
            String loo = tokFix[i];
            i++;
            System.out.println(loo);
            System.out.println(tokFix[i]); }

当我这样做时

System.out.println(loo);

它将正确输出数组中包含的每个字符串值

然而，当我做S

时

System.out.println(tokFix[i]);

它只会给我所有空值的输出

导致这种事情发生的两者有什么区别？

代码：

    public static String[] parseFixMsg(String fixMsg1,String fixMsg2){
        int i = 0;
        int size = getArraySize(fixMsg1);
        String[] tokFix = new String[size];
        StringTokenizer st = new StringTokenizer(fixMsg2,(Character.toString((char)01))+"]");
        st.nextToken();
    while (st.hasMoreTokens()) {
        tokFix[i] = st.nextToken();
        String loo = tokFix[i];
        i++;
        System.out.println(loo);
        System.out.println(tokFix[i]); }
    return tokFix;  
}


public static int getArraySize(String fixMsg){
    int size = 1;
     StringTokenizer st = new StringTokenizer(fixMsg,(Character.toString((char)01))+"]"); 
     st.nextToken();
        while (st.hasMoreTokens()) {
            st.nextToken();
            size+=1;
        }
        return size;
}

Answer 1

i++;

指向sys.out语句中的下一个元素。在循环结束时做++ i。

Answer 2

您需要稍微移动下面提到的行，因为您在打印前增加变量i。 sysout中的toFix[i]始终指向尚未初始化/分配的下一个元素：

System.out.println(tokFix[i]);

以下是您需要的更新代码

while (st.hasMoreTokens()) {
        tokFix[i] = st.nextToken();
        String loo = tokFix[i];
        System.out.println(tokFix[i]);
        i++;
        System.out.println(loo);
 }

Answer 3

以下是逐行解释正在发生的事情。让我们来看看i = 2：

的情况

while (st.hasMoreTokens()) {
    tokFix[i] = st.nextToken(); // Now tokFix[2] is not null
    String loo = tokFix[i]; // Again, so far so good; you're storing tokFix[2] to loo
    i++; // You've incremented i to 3 now! Here's your problem, as seen in the following:
    System.out.println(loo); // Prints out tokFix[2]
    System.out.println(tokFix[i]); // Prints out tokFix[3], which is null
}

正如其他人所说，只需将增量移动到循环的末尾。

while (st.hasMoreTokens()) {
    tokFix[i] = st.nextToken();
    String loo = tokFix[i];

    System.out.println(loo);
    System.out.println(tokFix[i]);

    i++; // Now we increment
}

Answer 4

       while (st.hasMoreTokens()) {
        tokFix[i] = st.nextToken(); // let's say i=1
        String loo = tokFix[i]; // now loo=  tokFix[1]
        i++;                     // now i=2
        System.out.println(loo);  // print loo value
        System.out.println(tokFix[i]); } // what happen here??? print tokFix[2]. But still not assign a value to that

所以将其更改为

        while (st.hasMoreTokens()) {
        tokFix[i] = st.nextToken();
        String loo = tokFix[i];            
        System.out.println(loo);
        System.out.println(tokFix[i]); 
        i++;
         }

为什么我的数组包含所有null？

4 个答案: